1,3-Bis(2-chlorophenyl)thiourea: a monoclinic polymorph

The title compound, C13H10Cl2N2S, represents a monoclinic polymorph of the previously reported orthorhombic form [Ramnathan et al. (1996 ▶). Acta Cryst. C52, 134–136]. The molecule is twisted with the dihedral angle between the benzene rings being 55.37 (7)°. The N—H atoms are syn to each other, which contrasts their anti disposition in the orthorhombic form. In the crystal, molecules assemble into zigzag chains along the c axis via N—H⋯S hydrogen bonds. Chains are connected into layers via C—H⋯Cl interactions, and these stack along the a axis.

The title compound, C 13 H 10 Cl 2 N 2 S, represents a monoclinic polymorph of the previously reported orthorhombic form [Ramnathan et al. (1996). Acta Cryst. C52, [134][135][136]. The molecule is twisted with the dihedral angle between the benzene rings being 55.37 (7) . The N-H atoms are syn to each other, which contrasts their anti disposition in the orthorhombic form. In the crystal, molecules assemble into zigzag chains along the c axis via N-HÁ Á ÁS hydrogen bonds. Chains are connected into layers via C-HÁ Á ÁCl interactions, and these stack along the a axis.

Comment
In connection with the synthesis and structural studies of thiocarbamides (Ho et al., 2005), diarylthioureas are sometimes isolated as the undesired hydrolysis by-product (Kuan & Tiekink, 2007). The title compound, (I), was isolated in crystalline form during the attempted synthesis of (C 6 H 4 Cl-o)N(H)C(═S)O-i-Pr. The structure of (I) is reported herein. A previously reported orthorhombic form of (I) exists in the literature (Ramnathan et al., 1996).
The molecular structure of (I), Fig. 1, is twisted about the central N-C bonds. With reference to the central plane through the CN 2 S chromophore [r.m.s. deviation = 0.0029 Å], the C2-benzene ring is almost perpendicular [dihedral angle = 85.20 (6)°] and the C8-ring is twisted [dihedral angle = 49.32 (6)°]; the dihedral angle between the benzene rings is 55.37 (7)°. The amide-H atoms are syn to each other. The syn conformation observed for the thiourea chromophore in (I) is quite distinct to that found in the orthorhombic polymorph (Ramnathan et al., 1996).
In the orthorhombic form of (I), the amide-H atoms are anti to each other. This key difference between the molecular structures in the two polymorphs is highlighted in the overlay diagram shown in Fig. 2. The anti orientation allows for the formation of eight-membered {···HNCS} 2 synthons in the crystal packing in the orthorhombic polymorph. By contrast, the crystal structure of (I) features supramolecular zigzag chains along the c axis mediated by N-H···S hydrogen bonds (Table   1 and Fig. 3); the S1 atom is bifurcated. Chains assemble into layers by C-H···Cl interactions (Fig. 4) and the layers thus formed stack along the a axis (Fig. 5).

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.95 Å) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2U eq (C). The N-bound H-atoms were located in a difference Fourier map but were refined with a distance restraint of N-H = 0.88±0.01 Å, and with U iso (H) = 1.2U eq (N).
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level. Fig. 2. Overlay diagram of (I) (shown in blue) with the two independent molecules found in the orthorhombic polymorph (see text), shown in red and green. The central thiourea fragments have been fitted.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Cl2 0.95110 (